Error: "The Only Proof Is That There Is No Proof!"

An assertion is either true, or non-true. If it's true, the person
asserting it must be able to show it's true, thanks to a proof. This
proof can require a more or less long reasoning, or on the contrary be a
return to a simple observation (like showing one's right hand to someone who
doubts our assertion "My right hand has five fingers"). But in any case,
during a philosophical debate, we must be able to prove what we assert.

In my debates, I sometimes encounter (especially with Atheists) people who
invoke as "proof", the very absence of proof!

A frequent variant of this error is to try to hide the absence of proof,
by claiming the accused himself eliminated that proof! Of course, the
accuser never explains how come he knows about these "proofs", even though
no trace of them can be found! Since no facts are required to make accusations
using this method, it's a favorite of conspiracy theorists.

Excuse me for a moment, I have to stop writing this article to make an urgent
phone call! I must call the police, since you just killed your grandmother and
robbed a bank! The proof? Well, since you're a very crafty criminal, you've
wiped out all traces of your crimes, therefore you're guilty! Hello? Police?

;-)

Seriously, in a philosophical debate, you just need to say:

Quod gratis asseritur, gratis negatur.
("What is asserted without proof, can be rejected without proof.")